It is proposed to investigate the mechanism of initiating ureteral peristalsis in the multicalyceal kidney of the pig. In these studies the contribution of the individual calyceal contractility will be examined in the context of a pyeloureteral pacemaker system. Unobstructed and hydronephrotic kidneys will be compared in vivo by measurement of renal pelvic and calyceal pressure, ureteral electromyogram at the obstructed site, bolus volume, ureteral diameter, and flow-velocity of the bolus. In vitro studies will be carried out concurrently in order to record the spatial and temporal characteristics of intrarenal smooth muscle in the control and hydronephrotic kidney.